linux-kernel - Re: [PATCH] clk: Re-evaluate clock rate on min/max update

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Message-ID: <20170428071743.GL30730@tbergstrom-lnx.Nvidia.com>
Date:   Fri, 28 Apr 2017 10:17:43 +0300
From:   Peter De Schrijver <pdeschrijver@...dia.com>
To:     Stephen Boyd <sboyd@...eaurora.org>
CC:     Michael Turquette <mturquette@...libre.com>,
        <linux-clk@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] clk: Re-evaluate clock rate on min/max update

On Thu, Apr 13, 2017 at 10:48:19AM +0300, Peter De Schrijver wrote:
> On Wed, Apr 12, 2017 at 09:46:05AM -0700, Stephen Boyd wrote:
> > On 03/21, Peter De Schrijver wrote:
> > > Whenever a user change its min or max rate limit of a clock, we need to
> > > re-evaluate the current clock rate and possibly change it if the new limits
> > > require so. To do this clk_set_rate_range() already calls
> > > clk_core_set_rate_nolock, however this won't have the intended effect
> > > because the core clock rate hasn't changed. To fix this, move the test to
> > > avoid setting the same core clock rate again, to clk_set_rate() so
> > > clk_core_set_rate_nolock() can change the clock rate when min or max have
> > > been updated, even when the core clock rate has not changed.
> > 
> > I'd expect some sort of Fixes: tag here? Or it never worked!?
> 
> I don't think this ever worked.
> 
> > 
> > > 
> > > Signed-off-by: Peter De Schrijver <pdeschrijver@...dia.com>
> > 
> > I seem to recall some problems here around rate aggregation that
> > we fixed after the patches merged. Sorry, but I have to go back
> > and look at those conversations to refresh my memory and make
> > sure this is all fine.
> > 
> > Are you relying on the rate setting op to be called with the new
> > min/max requirements if the aggregated rate is the same? I don't
> > understand why clk drivers care.
> > 
> 
> No. But I do rely on the rate setting op to be called when a new min or max
> rate would cause the rate to be changed even when there is no new rate request.
> 
> Eg:
> 
> min = 100MHz, max = 500MHz, current rate request is 400MHz, then max changes to
> 300MHz. Today the rate setting op will not be called, while I think it should
> be called to lower the rate to 300MHz.
> 

Any news on this? or do you think this is an unreasonable assumption?

Thanks,

Peter.